Sounds like we're mostly in agreement.^ I never meant to imply that DL shouldn't allow adding other FF#s at the time of purchase or train their agents better to avoid problems. My real gripe was that several of the posts here seemed to be implying that DL deliberately switches people's FF#s, which I just don't think is the case.

While DL should resolve the issues on their end, it's relatively easy (in my experience) to have problem-free crediting of DL flights to WP. Based on my personal experience and the numerous posts I've read, I suggest the following actions:

1. Make sure your NW FF# is the only one ever associated with the ticket. Even if you don't remember your DL FF#, don't "log in" to DL.com--it is probably saved in a browser cookie, and logging in will enter you DL FF#. If a phone rep asks for a DL#, just say you don't have one. If you buy a ticket through a third party (including online sites) make sure your DL# doesn't get entered--in many cases, booking a ticket on airline X will result in airline X's FF# being entered into your record. Cookies and server-hosted records at work again.

2. Until DL gets their act together to allow entry of other FF#s on their website when buying a ticket, e-mail DL to have the number input. A number of posts show that this is far quicker and easier than calling DL's phone line.

3. Make sure your NW# is on your DL BP before boarding--if you follow steps 1 and 2, it shouldn't be a problem. If it doesn't work out that way, then make sure it does before you board. Don't buy a GA saying that your NW# is in the record and miles will be credited to NW if a DL# is on the BP--the miles will really go to DL if the DL# is on the BP. Ask the agent to fully delete all FF# info and re-enter your NW#.